You've been checkstyled!

Change-Id: I0425764b2f3b07bc224a387ab7d544c6b360c691

+/*
+ *  Copyright 2016 Open Networking Laboratory
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.onosproject.ui;
+
+import org.onosproject.ui.model.topo.UiTopoLayout;
+
+import java.util.List;
+
+/**
+ * Service for managing {@link UiTopoLayout} instances.
+ */
+public interface UiTopoLayoutService {
+
+    /**
+     * Returns the list of available layouts.
+     *
+     * @return available layouts
+     */
+    List<UiTopoLayout> getLayouts();
+
+    /**
+     * Adds a layout to the system.
+     *
+     * @param layout the layout to add
+     * @return an indication of success
+     */
+    boolean addLayout(UiTopoLayout layout);
+
+    /**
+     * Removes a layout from the system.
+     *
+     * @param layout the layout to remove
+     * @return an indication of success
+     */
+    boolean removeLayout(UiTopoLayout layout);
+
+}

+/*
+ *  Copyright 2016 Open Networking Laboratory
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+
+package org.onosproject.ui.model.topo;
+
+import org.onosproject.net.region.Region;
+
+/**
+ * Represents a specific "subset" of the UI model of the network topology
+ * that a user might wish to view. Backed by a {@link Region}.
+ */
+public class UiTopoLayout {
+
+    private Region backingRegion;
+
+}

+/*
+ *  Copyright 2016 Open Networking Laboratory
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+
+package org.onosproject.ui.impl.topo;
+
+import org.apache.felix.scr.annotations.Activate;
+import org.apache.felix.scr.annotations.Component;
+import org.apache.felix.scr.annotations.Deactivate;
+import org.apache.felix.scr.annotations.Service;
+import org.onosproject.ui.UiTopoLayoutService;
+import org.onosproject.ui.model.topo.UiTopoLayout;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.List;
+
+/**
+ * Manages the user interface topology layouts.
+ * Note that these layouts are persisted and distributed across the cluster.
+ */
+@Component(immediate = true)
+@Service
+public class UiTopoLayoutManager implements UiTopoLayoutService {
+
+//    private static final ClassLoader CL =
+//            UiTopoLayoutManager.class.getClassLoader();
+
+    private final Logger log = LoggerFactory.getLogger(getClass());
+
+    @Activate
+    public void activate() {
+        // TODO: implement starting stuff
+        log.info("Started");
+    }
+
+    @Deactivate
+    public void deactivate() {
+        // TODO: implement stopping stuff
+        log.info("Stopped");
+    }
+
+
+    @Override
+    public List<UiTopoLayout> getLayouts() {
+        // TODO: implement
+        return null;
+    }
+
+    @Override
+    public boolean addLayout(UiTopoLayout layout) {
+        // TODO: implement
+        return false;
+    }
+
+    @Override
+    public boolean removeLayout(UiTopoLayout layout) {
+        // TODO: implement
+        return false;
+    }
+}

@@ -14,31 +14,43 @@
  *  limitations under the License.
  */
 
-package org.onosproject.ui.impl.topo.model;
+package org.onosproject.ui.impl.topo;
 
+import org.onosproject.ui.UiTopoLayoutService;
+import org.onosproject.ui.impl.UiWebSocket;
+import org.onosproject.ui.impl.topo.model.UiSharedTopologyModel;
+import org.onosproject.ui.model.topo.UiTopoLayout;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 /**
- * Base class for modeling the Topology View layout.
+ * Coordinates with the {@link UiTopoLayoutService} to access
+ * {@link UiTopoLayout}s, and with the {@link UiSharedTopologyModel} which
+ * maintains a local model of the network entities,
+ * tailored specifically for displaying on the UI.
  * <p>
  * Note that an instance of this class will be created for each
- * {@link org.onosproject.ui.impl.UiWebSocket} connection, and will contain
+ * {@link UiWebSocket} connection, and will contain
  * the state of how the topology is laid out for the logged-in user.
  */
-public class UiTopoLayout {
+public class UiTopoSession {
     private final Logger log = LoggerFactory.getLogger(getClass());
 
     private final String username;
+    private final UiWebSocket webSocket;
     private final UiSharedTopologyModel sharedModel;
 
     private boolean registered = false;
 
+    private UiTopoLayoutService service;
+    private UiTopoLayout layout;
+
     /**
      * Creates a new topology layout.
      */
-    public UiTopoLayout(String username) {
+    public UiTopoSession(String username, UiWebSocket webSocket) {
         this.username = username;
+        this.webSocket = webSocket;
         this.sharedModel = UiSharedTopologyModel.instance();
     }
 
@@ -60,6 +72,7 @@ public class UiTopoLayout {
     public void destroy() {
         if (!registered) {
             sharedModel.unregister(this);
+            registered = false;
         } else {
             log.warn("already unregistered");
         }
@@ -67,6 +80,6 @@ public class UiTopoLayout {
 
     @Override
     public String toString() {
-        return String.format("{UiTopoLayout for user <%s>}", username);
+        return String.format("{UiTopoSession for user <%s>}", username);
     }
 }

@@ -16,6 +16,7 @@
 
 package org.onosproject.ui.impl.topo.model;
 
+import org.onosproject.ui.impl.topo.UiTopoSession;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -28,20 +29,43 @@ public final class UiSharedTopologyModel {
     private static final Logger log =
             LoggerFactory.getLogger(UiSharedTopologyModel.class);
 
-    private static UiSharedTopologyModel singleton = null;
 
     private UiSharedTopologyModel() {
         // TODO: set up core model listeners and build the state of the model
     }
 
-    public void register(UiTopoLayout layout) {
-        log.info("Registering topology layout {}", layout);
-        // TODO: register the view
+    // TODO: Note to Thomas (or others)..
+    // Don't we have a common pattern for adding/removing listeners and
+    //  invoking them when things happen?
+
+
+    /**
+     * Registers a UI topology session with the topology model.
+     *
+     * @param session the session to register
+     */
+    public void register(UiTopoSession session) {
+        log.info("Registering topology session {}", session);
+        // TODO: register the session
+    }
+
+    /**
+     * Unregisters a UI topology session from the topology model.
+     *
+     * @param session the session to unregister
+     */
+    public void unregister(UiTopoSession session) {
+        log.info("Unregistering topology session {}", session);
+        // TODO: unregister the session
     }
 
-    public void unregister(UiTopoLayout layout) {
-        log.info("Unregistering topology layout {}", layout);
-        // TODO: unregister the view
+    /**
+     * Bill Pugh Singleton pattern. INSTANCE won't be instantiated until the
+     * LazyHolder class is loaded via a call to the instance() method below.
+     */
+    private static class LazyHolder {
+        private static final UiSharedTopologyModel INSTANCE =
+                new UiSharedTopologyModel();
     }
 
     /**
@@ -49,11 +73,7 @@ public final class UiSharedTopologyModel {
      *
      * @return the singleton topology model
      */
-    public static synchronized UiSharedTopologyModel instance() {
-        if (singleton == null) {
-            log.info("Instantiating Singleton.");
-            singleton = new UiSharedTopologyModel();
-        }
-        return singleton;
+    public static UiSharedTopologyModel instance() {
+        return LazyHolder.INSTANCE;
     }
 }